Machine tool cutting indication and control

ABSTRACT

Circuit means are provided for sensing the no load power into an electrical motor for driving machine tool and storing an electrical signal representative thereof. Power input in response to loading of said motor is also sensed. Circuit means are provided responsive to the difference in the no load and load power signals to provide a resultant signal varying in accordance with the magnitude of the difference. The existence of the signal indicates contact of the cutting tool with the workpiece and the magnitude of such signal indicates the degree of engagement.

United States Patent Inventor Malcolm H. Pitman Scotia, N.Y.

Appl..No. 803.203

Filed Feb. 28, i969 Patented Aug. 3, 1971 Assignee General ElectricCompany MACHINE TOOL CUTTING INDICATION AND CONTROL 7 Claims, 1 DrawingFig.

US. Cl 82/] R, 77/321, 340/267 R Int. Cl 1323b 3/06 Field of Search82/1, 2;

[56] References Cited UNITED STATES PATENTS 2,600,453 6/1952 Weingart82/] Primary Examiner Francis S. Husar Attorneys-Paul A. Frank, John F.Adhern, Julius J.

Zaskalicky, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. FormanABSTRACT: Circuit means are provided for sensing the no load power intoan electrical motor for driving machine tool and storing an electricalsignal representative thereof. Power input in response to loading ofsaid motor is also sensed. Circuit means are provided responsive to thedifference in the no load and load power signals to provide a resultantsignal varying in accordance with the magnitude of the difference. The

existence of the signal indicates contact of the cutting tool with thework iece and the magnitude of such signal indicates the degree ofengagement.

MACll-llllNlE TOOL CUTTING INDICATION AND CONTROL MACHINE TOOL CUTTINGINDICATION AND CONTROL The present invention relates to apparatus foruse with machine tools for sensing cutting action, and the degreethereof, of a cutting tool thereon.

The high cost of modern machine tools such as lathes, milling machines,planars and the like, particularly when automatically controlled, hascreated a need for equipment which will log the time that such machinesare performing a machining operation. It has been found that theutilization of some such machines is not high enough to yield anadequate return on the investment they represent. To improve utilizationof such machine tools certain information is required that is bestgathered by automatic data logging equipment. Conventional recorderswill log the time that the spindle of a machine tool to which theworkpiece is attached is turning but such time may be and usually isquite different from the actual cutting or machining time of the machinetool.

Accordingly, an object of the present invention is to provide a simple,effective and highly reliable apparatus for providing automatically anindication of time that a machine tool is performing a machiningoperation.

Another object of the invention is to provide a versatile machine toolcutting indication apparatus which may be attached to most any kind of amachine tool.

Another object is to provide apparatus of the character described whichis highly sensitive in response to the performance of machiningoperations on a machine tool.

In automatically operated machine tools it is desirable in order to savetime to rapidly advance cutting tools toward engagement with a workpieceand thereafter provide the desired rate of advance thereof into theworkpiece.

A further object of the present invention is to provide apparatus whichproduces signals which may be used not only to terminate a rapid advanceof a cutting tool into a workpiece before appreciable penetration hasbeen made, but also to provide the proper rate of advance of the cuttingtool into the workpiece to achieve efficient machining of the workpiece.

In accordance with an illustrative embodiment of the present inventionas applied to a machine too] there is provided means for sensing theno-load power into an electrical motor for driving the machine tool andstoring an electrical signal representative thereof. Power input inresponse to loading of said motor is also sensed. Circuit means areprovided responsive to the difference in the noload and load powersignals to provide a resultant signal varying in accordance with themagnitude of said difference. The existence of the signal indicatescontact of the cutting tool with the workpiece and the magnitude of suchsignal indicates the degree of engagement.

The novel features which are believed to be characteristic of thepresent invention are set forth in the appended claims. The inventionitself, however, together with further objects and advantages thereofmay best be understood by reference to the following description takenin connection with the accompanying drawings wherein:

The FIGURE shows a perspective view of a workpiece being machined by acutting tool mounted on a toolholder assembly and a block diagram partlyin schematic form indicating control apparatus of the present invention.

Referring now to the FIGURE, there is shown portions of a machine tool110 and apparatus 111 for providing a signal responsive to the loadingof an electric motor driving the machine tool. A metallic workpiece 12is supported in a workpiece holder ll. The workpiece holder ismechanically coupled through a gear drive 2 to drive motor l3 whichdrives the workpiece 12 in the direction indicated by the arrow 3. Acutting tool t is also shown mounted in a toolholder assembly 15. Thetoolholder assembly l5 includes a toolholder post M and a toolholder bed17 which is mounted on a pair of parallel guideways llti parallel to theaxis of rotation of the workpiece. The toolholder bed is movable alongthe guideways M by means of a screw drive llfl engaging the bed 117 atone end thereof and driven at the other end thereof from the gear drive2. The cutting tool d is mounted to the front end of a toolholder l9which in turn is clamped to a toolholder post id. The toolholder post 1%is slidably mounted on a pair of grooves in the bed 117 which isperpendicular to the guideways llli. A screw member 7 is provided, oneend of which engages the post M and the other end of which engages theupright side portion of the bed 1'? and includes a knob d for turningthe screw member for effecting engagement and disengage ment of thecutting tool d with the workpiece 112. The means described above andshown in the drawings for rotating the workpiece and driving the cuttingtool are conventional.

The apparatus 111 includes a power transducer 20 for providing the DCoutput representative of power input from the AC power lines 211. Such adevice may be a Hall effect semiconductor device in which the inputs,corresponding to current and voltage in a transmission line, produce anoutput which is proportional to the product of the component of thecurrent in phase with the voltage of the AC power line 211. In thisFIGURE the power transducer 20 is a three-phase wattmeter transducer andmay be, for example, a PT series manufactured by the RW. Bell Company,line. of Columbus, Ohio. The cable 22 from the input terminals of thetransducer connects to the three-phase power input lines 21 by means ofa coupling unit 23 which may include current transformers and directconnections to the lines 21 to provide voltage signals. The output ofthe transducer 20 is applied to the input of a wide band differentialamplifier 30 having a high input impedance and may be Basic Model No.3064 General Purpose Operational Amplifiers manufactured by the BurrBrown Research Corporation of Tuscon, Aria. Amplifier has a pair ofinput terminals 311 and 32, terminal Ell of which is connected to theground or common terminal of the power supply for the amplifier andterminal 32 is connected to the output of the wattmeter through aresistance 33. Output from the amplifier 30 is provided between outputterminal 34 and ground. Terminal 35 is connected to the positiveterminal of a unidirectional source, hereinafter referred to as B+ andterminal 36 is connected to the negative terminal of a unidirectionalsource, hereinafter referred to as B-. The other terminals of saidsources are connected to ground. A balancing potentiometer 37 isprovided for balancing the input and output signals of the amplifier,that is, to provide zero output in relation to ground for apredetermined output to the amplifier 30. A resistance 38 is connectedbetween the output terminal 34 and the ungrounded input terminal 32. Theratio of the resistance 38 to the input resistance'33 determines theamplification or gain of the amplifier 30. A capacitor 39 is provided inshunt with the resistance 3% to bypass noise.

The output of the amplifier 30 is applied to another broad banddifferential amplifier Ml which also may be a Basic Model No. 3064 madeby the Burr Brown Research Corporation of Tuscon, Ariz. The amplifier d0includes a pair of input terminals M and 42, terminal ll of which isconnected to ground, and terminal 42 of which is connected through a normally closed contacts d3 of a relay 44 to one terminal of a variableresistance 45, the other terminal of which is connected to the outputterminal 3d of the amplifier 30. Terminal 4b is connected to 8+ andterminal W is connected to 8-. Output is obtained between outputterminal 48 and ground. A balancing potentiometer W is connected to theamplifier 40 to provide balance between the input and output to theamplifier 40. The potentiometer 49 is adjusted to provide a zero outputin relation to ground for a predetermined input to the amplifier. Alarge capacitor fail in this particular example a 2- microfaradcapacitor, of the polystyrene type having low internal leakage isconnected between the output terminal 48 and the ungrounded inputterminal 42. The leakage resistance of such capacitor is of the order of10 ohms. Also, as the input impedance of the amplifier 40 is of theorder of ohms, the combination of the capacitor 50 and the dischargeresistances associated with the capacitor provide a very long timeconstant of the order of 2 percent loss in voltage in 4 hours. Thereason for such a large time constant will be apparent from thedescription below. A resistance 51 is connected between the outputterminal 48 and the contact of the normally closed contacts 43 remotefrom the input terminal 42 of the amplifier 40. The ratio of theresistance 51 to the variable resistance 45 determines the gain of theamplifier 40. The gain of the amplifier 40 is set to be slightly greaterthan unity. The gain of the amplifier determines the threshold level ofpower input to the motor 13 above no-load power input at which a signalis obtained from a subtractive network represented by resistors 52 and53 to provide output to a driver amplifier 60 for operation of autilization circuit such as a meter or a proportion control circuit 69giving a linear output above no load. A pair of diodes 55 and 56 areprovided connected in parallel and reversely poled between junction ofresistances 45 and 51 and ground for the purpose of limiting theexcursion of signal applied to the input of the amplifier 40 betweenvoltages represented by the forward drops of the diodes or a pluralityof such diodes connected in series to give a greater range for suchexcursions. A capacitor 57 is provided in shunt between the outputterminal 34 of the amplifier 30 and ground to filter noise from theoutput signal.

Signals from the output of amplifier 30 are directed into two channelsto the input of amplifier 60. One channel includes variable resistance45, the normally closed contact 43, the amplifier 40 and the resistance52. The voltage reference amplifier 40 reverses the polarity of thesignal applied to the input thereof. Accordingly, resistances 52 and 53form a subtractive network for developing an output between the input toamplifier 60 and ground representing the difference of the signalsapplied at the other ends thereof and ground.

To operate the machine tool the ganged contacts 61, 62, 63 are closed toenergize the motor 13. Simultaneously with the closing of the contacts61. 62, 63 a fourth contact 64 ganged therewith is closed and energizesa time delay relay 65 connected to power lines 67. The time delay 65relay in turn closes normally open contact 68, after a predeterminedtime period, for example a few seconds, connected in series with thecoil of the relay 44 to the power-line 67. Energization of the relay 44opens the normally closed contact 43. lmmediately upon closing of gangedcontacts 61, 62, and 63 in the power lines 21, power flow into the motor13 is sensed by the transducer 20 and provides a signal to the referenceamplifier 40. After a few seconds after transients have subsided thevoltage appearing at the output of the amplifier 40 and stored thereonby the long time constant of the discharge circuit of capacitor 50 is arepresentative of the no-load power being supplied to the motor. Thevoltage is of positive polarity in relation to ground and is slightlygreater than the voltage appearing at the output of the amplifier 30.Should the cutting tool be advanced into the workpiece to perform amachining operation thereon, the power required to be supplied from thepower lines to the motor increases. Such increase in power appears as anincrease in voltage across the output terminals of the transducer 20.Such voltage is amplified by the amplifier 30 and appears as a negativesignal in relation to ground at the output thereof. The signal isblocked from passing to the reference amplifier 40 by the contacts 43which are now open. Such signal, however, appears across resistance 53and combines with the output from the reference amplifier 40 appearingacross resistance 52 and ground. Accordingly, the net signal appearingacross the terminal ".0 at the input of amplifier 60 and ground is thedifference between the two signals stored, no load signal and'the loadsignal. Should the power input to the motor exceed the threshold levelset by the gain of the amplifier 40, a net signal appears at the inputof the amplifier 60. Such net signal is amplified by amplifier 60 toprovide an indication of degree engagement of the machine tool with aworkpiece. Such signal can be further amplified by amplifier to providea driving signal to effect closure of the contacts of a reed relay 81which in turn can initiate operation of timer 82.

The amplifier 60 may supply a signal proportional to the amount ofloading the machine tool produces on the workpiece. Such a signal couldbe used for setting the level of optimum cutting load on the machinetool 10. Each of the output amplifiers 60 and 80 may be Basic Model No.31 19 amplifiers made by Burr Brown Research Corporation of Tuscon,Ariz. The amplifier 60 includes a pair of input terminals 70 and 71 oneof which is connected to ground and the other of which, namely 70, isconnected to the junction of resistances 52 and 53. 8+ and 5- lines areconnected respectively to terminals 72 and 73. Output is taken betweenoutput terminal 74 and ground. A Zener diode 75 is connected in shuntacross the input terminal 70 and the output terminal 74 to provide alimit to the positive excursion of the output thereof for protection ofinstruments connected between output 74 and ground and, similarly, aclamping diode 76 may be connected across the input and output terminal70 and 74 to limit the excursion of the output voltage in the negativedirection to the value of the forward drop in diode 76. Gain of theamplifier 60 is controlled by the ratio of the resistance 77, connectedbetween the input terminal 70 and output terminal, and the inputresistances 52 and 53. A shunting capacitor 78 to filter noise may beprovided.

The output of the amplifier 60 is applied through resistance 79 to theinput terminal 83 of amplifier 80, the other input terminal 84 of whichis connected to ground. 8+ and B- lines are connected respectively toterminals 85 and 86. Output is taken between the output terminal 87 andground. A Zener diode 88 is connected between the input and the outputterminals 83 and 87 to limit the negative excursion of the outputvoltage and similarly a diode 89 is connected in shunt between the inputand the output terminals 83 and 87 to limit the excursion of the outputin the positive direction to a value less than the forward drop of thediode 89. A capacitor 90 to bypass noise is provided in shunt betweenthe input and output terminals 83 and 87. The output from amplifier 80is applied through a diode 91 to one terminal of the solenoid of a reedrelay 82, the other terminal of which is connected to ground. A diode 92is shunted with a solenoid of the reed relay 81 to dampen any switchingtransients produced in the opening of the solenoid circuit of the relay.The contacts of the reed relay 81 are connected to a utilization whichmay be a timer 82 as shown.

The apparatus described is particularly applicable to systems usinginduction motors. The excitation or no-load current of such inductionmotors is substantially in phase quadrature with the driving voltage. Asthe loading increases, the resultant input current changes in phasewithout appreciably changing in amplitude. However, the power factor ofthe input changes at a very rapid rate for increase in load untilloading of the induction motor approaches a substantial percentage ofthe full load rating. Accordingly, apparatus which is respon-.

sive to current in the power input lines of the induction motor wouldnot be sufficiently sensitive to provide a good source of timing signalto indicate loading thereon. it should be noted that in most machinetools the loading of the motor normally does not exceed a fraction ofthe rated output of the motor. In machine tools using induction motors lhave found that satisfactory operation is obtained with the gain of theamplifier 40 set to provide an output which is 2 percent greater thanthe input. Accordingly, when the loading of the motor 13 exceeds 2percent of the no-load power input to the motor, a signal is developedat the input terminals of the amplifier 60. The gain of the amplifier 80can be set to be quite high and hence responds substantiallyinstantaneously to a small signal at the input of amplifier 60 once theload current exceeds the threshold. Of course, the threshold would beset to satisfy the requirements of the application to which theapparatus is put.

While the apparatus has been described in connection with an AC motor,it is equally applicable to drive systems in which DC motors areutilized. Also, as the loading on the motor 13 changes, the output ofthe amplifier 60 varies in accordance therewith. Such output is appliedto the proportion control circuit. The proportion control circuit mayinclude a source of reference voltage of variable magnitudecorresponding to various degrees of cutting loading of the machine tool.The departure of the voltage derived from the output of the amplifier 60from the aforementioned reference voltage, could be used as an errorsignal for a servomechanism to provide a proper engagement of themachine tool with the workpiece for efficient and effective cuttingaction.

While the invention has been described in a specific embodiment, it willbe appreciated that many modifications may be made by those skilled inthe art and I intend by the appended claims to cover all suchmodifications and changes as fall within the true spirit and scope ofthe invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination with a machine tool which includes a workpiece holderand a cutting tool, an electric motor for moving the workpiece holder inrelation to the cutting tool, and means for advancing the workpieceholder in relation to the cutting tool to bring a workpiece attached tothe workpiece holder into engagement with the cutting tool forperforming a machining operation on the workpiece, apparatus forproviding an indication of engagement of the tool with the workpiececomprising a first signal means connected to said electrical motor forsensing the no-load power input to said electrical motor and deriving afirst unidirectional electrical signal the amplitude of whichcorresponds to said no-load power input,

a storage means connected to said first signal means for storing saidfirst unidirectional signal,

a second signal means connected to said storage means for sensing thepower input to said electrical motor in response to loading of saidmotor and for providing a second unidirectional signal, the amplitude ofwhich varies with and corresponds to the loading of said motor, noloadmeans connected to said storage means and to said second signal meansfor combining said stored first unidirectional signal and said secondunidirectional electrical signal to develop a third unidirectionalsignal the amplitude of which varies in accordance with the amplitude ofthe difference of said first and second electrical signals corresponding to the difference in said no-load and load power inputrespectively to said motor, whereby an indication of the engagement ofsaid tool with said workpiece is obtained.

2. The combination of claim 1 including means connected to saidcombining means responsive to a predetermined level of said third signalcorresponding to a predetermined loading of said motor by the engagementof said tool with said workpiece to provide an indication of theengagement of said tool with said workpiece.

3. The combination of claim 1 in which the factor of proportionality insaid first signal means between no-load power input to the amplitude ofsaid first unidirectional signal is greater than the factor ofproportionality in said second signal means between the load power inputto the amplitude of second unidirectional signal, whereby zero amplitudeof said third unidirectional signal corresponds to a threshold level ofloading of said motor, said threshold level being determined by thedifference in said factors of proportionality.

4. The combination of claim 2 in which said means responsive to saidthird unidirectional signal is a timer.

5. In combination with a machine tool which includes a workpiece holderand a cutting tool, an electric motor for rotating the workpiece holderin relation to the cutting tool, and means for advancing the workpieceholder in relation to the cutting tool to bring a workpiece attached tothe workpiece holder into engagement with the cutting tool forperforming a machi ning operation on the workpiece, apparatus forproviding an indication of engagement of the tool with the workpiececomprising means connected to a source of electrical energy forelectrically energizing said motor,

means coupled to the input circuit of said electric motor for sensingpower flowing thereto and providing a first unidirectional signalcorresponding to the power flowing to said motor,

a pair of channels, each having an input circuit and an output circuit,

means for applying said first unidirectional signal to the inputcircuits of said channels,

one of said channels including an amplifier for developing a secondunidirectional signal in response to said first unidirectional beingapplied thereto and being capable of providing said secondunidirectional signal at the output thereof for a long period of timewhen said first predetermined input is no longer being applied thereto,

means connected to the input circuit of said one channel fordisconnecting the input circuit of said one channel a short time afterthe energization of said motor and before loading is applied theretowhereby said first signal is applied solely to the input circuit of saidother channel,

said other channel providing a third electrical signal at the outputthereof in response to said first electrical signal, the amplitude ofwhich varies with and corresponds to the loading of said motor,

means connected to the output circuits of said channels fordifferentially combining the outputs of said channels and for deriving afourth unidirectional signal the amplitude of which varies in accordancewith the amplitude of the difference of said second and third electricalsignals corresponding to the difference in said no-load and load powerinput respectively to said motor, whereby an indication of theengagement of said tool with said workpiece is obtained.

6. The combination of claim 5 in which said amplifier includes acapacitance of high internal impedance connected between the output andinput circuits of said amplifier, and said amplifier also includes ahigh input impedance whereby said capacitance retains electrical chargeover a long period of time and provides a constant unidirectionalelectrical output corresponding to no-load power input to said motorwhen said first signal is disconnected from said amplifier.

7. The combination of claim 5 in which said electric motor is aninduction motor.

1. In combination with a machine tool which includes a workpiece holderand a cutting tool, an electric motor for moving the workpiece holder inrelation to the cutting tool, and means for advancing the workpieceholder in relation to the cutting tool to bring a workpiece attached tothe workpiece holder into engagement with the cutting tool forperforming a machining operation on the workpiece, apparatus forproviding an indication of engagement of the tool with the workpiececomprising a first signal means connected to said electrical motor forsensing the no-load power input to said electrical motor and deriving afirst unidirectional electrical signal the amplitUde of whichcorresponds to said no-load power input, a storage means connected tosaid first signal means for storing said first unidirectional signal, asecond signal means connected to said storage means for sensing thepower input to said electrical motor in response to loading of saidmotor and for providing a second unidirectional signal, the amplitude ofwhich varies with and corresponds to the loading of said motor, no-loadmeans connected to said storage means and to said second signal meansfor combining said stored first unidirectional signal and said secondunidirectional electrical signal to develop a third unidirectionalsignal the amplitude of which varies in accordance with the amplitude ofthe difference of said first and second electrical signals correspondingto the difference in said no-load and load power input respectively tosaid motor, whereby an indication of the engagement of said tool withsaid workpiece is obtained.
 2. The combination of claim 1 includingmeans connected to said combining means responsive to a predeterminedlevel of said third signal corresponding to a predetermined loading ofsaid motor by the engagement of said tool with said workpiece to providean indication of the engagement of said tool with said workpiece.
 3. Thecombination of claim 1 in which the factor of proportionality in saidfirst signal means between no-load power input to the amplitude of saidfirst unidirectional signal is greater than the factor ofproportionality in said second signal means between the load power inputto the amplitude of second unidirectional signal, whereby zero amplitudeof said third unidirectional signal corresponds to a threshold level ofloading of said motor, said threshold level being determined by thedifference in said factors of proportionality.
 4. The combination ofclaim 2 in which said means responsive to said third unidirectionalsignal is a timer.
 5. In combination with a machine tool which includesa workpiece holder and a cutting tool, an electric motor for rotatingthe workpiece holder in relation to the cutting tool, and means foradvancing the workpiece holder in relation to the cutting tool to bringa workpiece attached to the workpiece holder into engagement with thecutting tool for performing a machining operation on the workpiece,apparatus for providing an indication of engagement of the tool with theworkpiece comprising means connected to a source of electrical energyfor electrically energizing said motor, means coupled to the inputcircuit of said electric motor for sensing power flowing thereto andproviding a first unidirectional signal corresponding to the powerflowing to said motor, a pair of channels, each having an input circuitand an output circuit, means for applying said first unidirectionalsignal to the input circuits of said channels, one of said channelsincluding an amplifier for developing a second unidirectional signal inresponse to said first unidirectional being applied thereto and beingcapable of providing said second unidirectional signal at the outputthereof for a long period of time when said first predetermined input isno longer being applied thereto, means connected to the input circuit ofsaid one channel for disconnecting the input circuit of said one channela short time after the energization of said motor and before loading isapplied thereto whereby said first signal is applied solely to the inputcircuit of said other channel, said other channel providing a thirdelectrical signal at the output thereof in response to said firstelectrical signal, the amplitude of which varies with and corresponds tothe loading of said motor, means connected to the output circuits ofsaid channels for differentially combining the outputs of said channelsand for deriving a fourth unidirectional signal the amplitude of whichvaries in accordance with the amplitude of the difference of said secondand third electrical signals correspondiNg to the difference in saidno-load and load power input respectively to said motor, whereby anindication of the engagement of said tool with said workpiece isobtained.
 6. The combination of claim 5 in which said amplifier includesa capacitance of high internal impedance connected between the outputand input circuits of said amplifier, and said amplifier also includes ahigh input impedance whereby said capacitance retains electrical chargeover a long period of time and provides a constant unidirectionalelectrical output corresponding to no-load power input to said motorwhen said first signal is disconnected from said amplifier.
 7. Thecombination of claim 5 in which said electric motor is an inductionmotor.